The long-term objective of research performed in this lab will be to better understand how neurons within the ventrolateral medulla influence autonomic and respiratory functions. The nucleus ambiguus (NA), located within the ventrolateral medulla, contains some neurons that influence autonomic functions and others that influence respiratory functions. Some neurons within the NA send their axons in company with the vagus nerve, and, via which, they are largely directed to the heart. These neurons, known to be cholinergic, are capable of influencing autonomic functions. Other neurons within the NA send their axons to the spinal cord, where they terminate upon the phrenic nucleus, located in segments C3-5 of the cervical spinal cord. These neurons are considered capable of influencing respiratory functions. However, in addition, the NA contains other ambiguuo-spinal neurons that project their axons to all levels of the thoracic spinal cord. It has been presumed that these latter ambiguuo- spinal neurons may play a role in respiration, by influencing the function of intercostal muscles. In fact, however, very little is known regarding the NA projections to the thoracic cord! Consequently, to better understand these projections, the proposed research project will undertake the following specific aims: (1) To describe the spatial relationships existing between ambiguuo-vagal neurons and ambiguuo-spinal neurons. This aim will be accomplished in studies using fluorescent retrograde tracers. (2) To determine whether ambiguuo-spinal neurons are cholinergic, and thus similar to ambiguuo-vagal neurons. This aim will be accomplished through the immunohistochemical identification of those neurons containing the acetylcholine-synthesizing enzyme, choline acetyltransferase (ChAT). (3) To describe in detail ambiguuo-spinal terminations within the thoracic spinal cord, and the relationship that these terminations have upon: (a) motor neurons innervating intercostal muscles, and (b) sympathetic preganglionic neurons. This aim will be accomplished in studies involving a variety of orthograde and retrograde tracers. Information resulting from this project will make it possible to have a better understanding of medullary neurons that influence autonomic and respiratory functions.